An electronic control device such as engine control unit or automatic transmission control unit for a vehicle generally includes a housing having a plurality of housing members joined together to define therein a protection space (watertight space) and a circuit board accommodated in the protection space of the housing and mounting thereon various electronic components.
This type of electronic control device requires high waterproof performance for use in an engine room etc. of the vehicle. If the inner space of the housing is completely sealed, however, the housing and its sealing part may be subjected to excessive stress due to increase or decrease in the internal pressure of the housing. The application of such excessive stress becomes a cause of deterioration of durability and reliability.
It has thus been proposed to provide a so-called breathing filter by forming a vent hole in the housing member and fixing an air-permeable waterproof membrane in the vent hole (see, for example, Patent Document 1).